Current regulating system



Dec. 14, 1948. R. w. HOLMAN CURRENT REGULATING' SYSTEM Filed Jan. 24,1944 Patented Dec. 14, 1948 CURRENT REGULATING SYSTEM Robert W. Holman,Gary,

negle-Illinois Steel Corp of New Jersey Ind., assignor to Caroration, acorporation Application January 24, 1944, Serial No. 519,517

3 Claims.

This invention relates to a current regulating system, and particularlyto-an improved means for controlling the current supplied to theelectrolyte of electroplating equipment as the metal strip or similarwork continuously passes therethrough at a varying rate of speed.

It is now common practice to apply a coating, such as tin, to continuouslength metallic strip material, such as iron or steel, by electrolyticmeans. A coil of the uncoated strip is positioned on the entry end of anelectrotinning line and the strip as it is uncoiled passes throughvarious pieces of apparatus and finally into and through theelectroplating equipment. .Such an electrotinning line is usuallyoperated from a variable voltage system, and is started by increasingthe generator voltage until it overcomes the internal drop of thevarious motors so that the strip starts to move at a very low travelingspeed. The plating current and the line are then simultaneouslyincreased automatically by various electrical devices and circuits untilthe desired operating speed is obtained. Since the thickness of the tinor other coating deposited on the strip is a function of both time andspeed, the plating current required is determined by the speed of theline at which any given coating weight is to be applied to the strip.After these two factors have been ascertained, the total plating currentrequlre-' ments can be determined, but this does not necessarily meanthat heavier coatings cannot be applied or that the line cannot be runat a higher speed. Heavier coatings can be obtained at reduced linespeeds while on the other hand, lighter coatings can be obtained athigher or increased speeds. It will be understood that it is essentialonly that a proper relationship between the total plating current andthe speed be maintained for the desired coating weight, and it is to a,current control system for maintaining this relationship that thepresent invention relates.

Various means have been heretofore suggested and used for maintainingthis balance between the plating current and the line speed, but most ofthem have been unsatisfactory in that either the equipment required wasexpensive and necessitated special designing and construction, or wasnot fast enough in its action, that is, such equipment was usuallysluggish in its function. Such means as heretofore suggested and usedusually included a tachometer generator driven directly by one of thestrip contacted rolls of the line. Direct current output of thetachometer, which is in equal ratio to the speed of the line, was usedin conjunction with controlling apparatus to regulate plating current tothe anodes 01' the plating equipment. Since, as has been stated thatthe-speed of the strip versus plating current is extremely criticalinsofar as maintaining an [even coating weight is concerned, itnaturally anisms, and other devices. It has been found that V such acontrol is entirely too sluggish in its action as the time required foroperation of thevarious circuits and devices was a matter of minutes,whereas the time usually required'to slow down or speed up the line is amatter of seconds.

Accordingly, it is thegeneral object of the present invention to providean improved current control system for a power supply which willcompensate for relatively rapid variations of the load requirements,and, at the same time, a control system which is sensitive and, almostinstantaneous in its action thereby eliminating the disadvantages ofcontrols heretofore suggested and used.

It is a further object of this invention to provide an improvedelectrical system for controlling the current output of a generator orpowering means of electroplating equipment whereby the current output ofthe generator is varied as the speed of the strip varies.

It is still another object of the present inven' tion to provide animproved electrical system for controlling the current output of agenerator or powering means includin a specially designed saturablereactor which is simple and inexpensive in its construction and, 'at thesame time, eflicient and effective in its use.

Various other objects and advantages of this invention will be moreapparent in the course of the following specification and will beparticularly pointed out in the appended claims.

The accompanying drawing illustrates schematically an example ofapparatus embodying the principles of the present invention.

In this drawing, S indicates a continuous length of metallicstripmaterial or the work which is adapted to be passed continuously'throughan electrolyte L in a plating tank T for electroplating or depositing acoating, such as tin,

pose of illustration and that usually a plurality of generators are usedin such equipment. The negative armature lead of the generator 2 isconnected to a conventional type cathode bus bar 4 which, in turn, isconnected to a plurality of copper conductor rolls 5 arranged above theplatmg tanlr '1' through suitable brush arrangements (not shown) at eachindividual roll. There is also arranged at the bottom of the tank Tpreferably non-conductor rolls 6, and it will be understood that thestrip passes in a sinuous path over the conductor rolls 5 and thenon-conductor rolls 8 whereby vertically extending strip portions areprovided in the electrolyte and the tank, as the strip passestherethrough. Since the strip passes over the conductor rolls 5 whichare connected to the cathode bus bar it of the plating generator, itwill be obvious therefore that the strip is in effeet the cathode of theplating process.

There is arranged in the tank T and disposed in the electrolyte Ltherein between the vertical portions or the strip S, a plurality ofvertically extending cast tin anodes l or anodes consisting of the metalwhich is adapted to be applied to the strip. The anodes l are supportedpreferably by horizontal anode bridges ll arranged between the verticalpass-es of the strip and are connected to an anode bus bar 9 which, inturn, is connected to the positive lead of the armature 2. It will beseen that the armature 2 of the plating generator establishes anelectric current between the electrolyte L and the work or strip Sthrough a circuit which includes the conductor rolls d and anodes limmersed in the electrolyte, in a well known manner. It will beunderstood that the output of the armature 2 of the plating generator isdirectly proportional to the strength of its field 8 which is poweredthrough a circuit i0 by an exciting generator having an armature l2 anda field IS with a rheostat It included in the circuit for controllingthe strength of the field 3 01, the plating generator. The field E3 ofthe exciting generator is connected to a suitable regulator to, such asan electronic control, by the lines or circuit l6.

According to the present invention, there is provided a second orcontrol circuit having an especially constructed saturable reactor itwhich performs the function of delivering a reference voltage from thecathode bus bar 4 to the regulator IS in a manner now to be described.One side of the saturable reactor ll consists of a rectangular-shapedextension bar-like member l8 which is attached to the cathode bus bar 4,preferably by means of two leg portions l9. This arrangement provides inthe member i8, a direct current exactly proportioned to that existing inthe cathode bus bar 4. The other side of the saturable reactor llconsists of alternating current windings 2i and 22 arranged on the cores2d and which are connected to a suitable source of alternating currentsupply by means of lines 33 and 26. The alternating current windings 2iand 22 are connected in parallel with each other and with such polarityrelationship that they oppose each other so that no alternating currentwill be generated or communicated to the member it between the points Xand Y, and consequently to the cathode bus bar 4. There is con nected inseries with the windings 2| and 22, a variable resistor 25 which isutilized to regulate voltage to the primary of a transformer 26 which isalso arranged in the second or control circuit with the saturablereactor l1. When the electroplating line is in operation, it will beseen that direct current in proportion to the plating bus current willflow in the member i8, and as a result the reactance of alternatingcurrent windings 2| and 22 will be reduced thus allowing alternatingcurrent to flow into the second -circuit. The amount of alternatingcurrent passing into the second circuit when no direct current ispresent in member I8 is extremely small and of a negligible value and isonly of an amount required for magnetizing the cores 20. As alternatingcurrent passes through the second circuit, the voltage drop occurringacross the resistor at points A and B is multiplied or lncreased to ahigher value by means of the transformer 26. 'It will be obvious thatthe increased voltage supplied by the transformer 26 to the secondcircuit, at points C and D bears a dennite relationship to the inputvoltage at points Al. and B because of the ratio of the transformer 25.

There is also arranged in this second or control circuit and connectedto the secondary side oi the transformer 26, preferably a rectifier 2?for rectifying the alternating current supplied by this transformer sothat direct current is sup plied at points E and F in the lines 23 and23, respectively, of the circuit. If desirable, the voltage issuing fromthe rectifier 2t may be fil tered by use of a choke coil so. a condenser36 and a loading resistor 32 arranged in the circuit.

It will be seen that the voltage occurring bctween the points E and orbetween points and G is approximately proportional to the cur rent inthe member l8 and consequently the cathode bus bar l. In order to obtainsubstana tially straight line characteristics of the direct current inthe member it) versus the direct current voltage between points E and For E and in the secondary circuit. the cores ml of the saturable reactorll necessarily must have. a sharp knee in their saturation curve. Alsothe cores 20, as well as alternating current windings 2| and 22, must bedesigned to operate at a magnetic saturation to provide thecharacteristics desired. By operating these cores within certain rangesof saturation, the output between points E and-G is independent ofnormal power source fluctuations of the alternating current as suppliedto the saturable reactor I! by the lines 23 and 24.

In order to provide a voltage in the second or control circuitproportional to the load or the traveling speed of the strip S, there isprovided a tachometer generator 33 which is driven preferably by themain drive bridle R. of the line or any other roll contacted by thestrip as it passes through the line. The negative terminal or side 29 ofthe rectifier 21 is connected to the negative terminal'or side of thetachometer generator 33 by means of the line 34 thus forming in asenseone side of a loop in the control or secondary circuit. The positiveside or line 28 leading from the rectifier 27 is connected to theregulator l5 and also the positive side of the tachometer generator I:is connected to the regulator by means of the line through the rheostat38 and a resistor 31. Inother words, the line 28 together with the line35, the rheostat 38 and the resistor 31 constitute the other or positiveside of the loop in the control circuit.

As has been hereinbefore stated, the tachometer generator 33 supplies anelectric voltage to the secondary circuit in proportion to the speed ofthe strip 8 through the line. It will be seen that this voltage is inopposition to the voltage supplied to the second or control circuit bythe saturable react/or i1 together with the transformer 26 and therectifier 21 from the cathode bus bar 4. When the voltage in thesecondary circuit becomes unbalanced due to these opposed voltages, itis the purpose of the control or reg-- ulator I! to function so as toincrease or decrease the strength of the exciter field i3 of theexciting generator which, in turn, controls the held 3 of the platinggenerator so as to increase or decrease the amount of current suppliedto the load or the primary circuit for plating in a manner which willnow be described.

When the line is in operation and the strip is passing over theconductor rolls 5 and through the electrolyte L, current is supplied tothe anodes I from which it flows or is conducted through the electrolyteto the strip S and passes through the conductor rolls 6 and returns tothe plating generator by way of the cathode bus bar 4. The saturablereactor ll transmits into the secondary circuit by means of theassociated equipment, a voltage indication to the regulator it atterminal E which indication is in direct proportion to the platingcurrent in the cathode bus bar 4. As the strip is passing through theline, it will be seen that the tachometer generator is simultaneouslyrotated by the drive bridle rolls R and transmits a voltage indicationto the regulator or control l5 whici'i voltage is in direct relation tothe speed of travel of the strip. Under normal operating conditions, i.e., where the speed of the line is constantly maintained, all portionsof the control or secondary circuit will be in balance and the currenttherein will be flowing in an orderly and undisturbedmanner.

However, should the speed of the line be suddenly increased, thetachometer generator 33 will immediately transmit additional voltage tothe secondary or control circuit in opposition to the reference voltagesupplied thereto by the saturable reactor l'l thereby disturbing thebalance of the control circuit at regulator l5. This unbalance of thecircuit indicates to the regulator I! a need for an immediate increaseof plating current to compensate for the increased rate of travel of thestrip in order to apply the proper weight of coating thereon. Theregulator responds to this unbalanced voltage in the secondary circuitby increasing the strength of the held I: of the exciting generator.When the strength of the field i3 is increased, the exciter armature i2will automatically deliver more current to the shunt field 3 of theplating generator. As a result, it will be'seen that the platinggenerator will deliver more current to the plating circuit bus bars 4and 8.

It will be understood that the plating current must be limited to theamount required for emcient coating and this is accomplished by thesaturable reactor I! in the following manner. When the plating currentis increased in the bus bar 4, it will also be increased proportionatelyin the crosspiece or member l8 of the saturable reactor ll. Thisincrease of the current in the member l8 will cause an increase in theamount of alternating current flowing through the windings 2i and 22 ofthe saturable .reactor in a manner hereinbefore explained.

This increased flow of the alternating current through the windings 2|and 22 is reflected by a corresponding increase in the output of thetransformer 26 and the rectifier 21 at points E and F and since the line28 in which E is located is connected to the regulator i5, the voltagedelivered at E and to the regulator will not match the voltage suppliedto the regulator by the line 35 connected to the tachometer generator.As

long as this condition prevails, the regulator I5 will continue toincrease the plating current in the bus bars 4 and 9 due to thepredominating voltage in lines 34 and 35 or until the voltage betweenpoints E and G which is proportional to the plating current in bus bar texactly equals the voltage generated by the tachometer generator 33 inthe lines 34 and 35. When the reference voltage as supplied by thesaturable reactor i'l. equals or matches the voltage supplied by thetachometer generator 33 and the voltage in the secondary or controlcircuit is again balanced, the regulator i5 will automatically ceaseincreasing the plating current in the bus bars 4 and 9 by means of theexciting generator which controls the field of.the plating generator ina manner hereinbefqre described and stable conditions will prevail aslong as the line speed continues at its increased rate of travel.

It will be understood that the above described performance of thecontrol circuit and the devices occurs almost instantaneously to balancethe plating current against the speed oi the line. While the cycle ofoperation as above described relates to an increase in the line speed,it will be understood that the control circuit will function inidentically the same manner when the speed of the line decreases, infact, any deviation in the line speed including both acceleration anddeceleration will be reflected by unbalanced. voltages at the regulatori5 and corrected by the regulator in the manner as hereinbeioredescribed.

While the improved current regulating system of my invention is shownfor controlling the current supplied to the electrolyte of anelectrotinning line, it will be understood that such a regulating systemcan be used to regulate and maintain constant the direct current flow inthe direct current tie between any two alternating current systemsconnected for power interchange through an electronic mercury arcfrequency changer or to maintain constant current input to a motor fordriving tension reels or rolls. It will be seen that by use of thecurrent regulating system of the present invention that a high voltageproportional to the current is obtained while in other control systemsheretofore suggested and-used, millivolts are obtained.

While I have shown and described one specific embodiment of myinvention, it will be understood that this embodiment is merely for thepurpose of illustration and description and that various other forms anduses may be devised within the scope of my invention, as defined in theappended claims. i

Iclaim:

1. A system for regulating the current output of a generator connectedto a load including, in combination, a first circuit including a bus barconnected to the generator for conveying the dlrect current generatedthereby to the load, a second electric circuit including a, saturablereactor wherein the bus bar constitutes one side thereof withalternotlng current windings constituting the other side of the same, a.source of alternating current supply for said windings, said windingsbeing connected so that no alternoting current will be generated in thedirect current bus bar when alternating current is supplied to saidwindings whereby a. voltage will be obtained in said second circuitproportional to the current in said first circuit and said bus bur, e.resistor connected in series with said windings, means for multiplyingthe voltage drop occurring across sold resistor, means for rectifyingsaid multiplied voltage, means for obtaining a voltage in said secondcircuit proportional to that required by the load and in opposition tosaid multiplied voltage, and means responsive to the direction ofcurrent *fiow'in said second circuit for varying the output of saidgenerator.

2. in a, current control system having a bus bur for supplying directcurrent to the load from a generator, a. secondary circuit including osatureble reactor wherein the bus bar constitutes one side of thesuturoble reactor with ulternat ingcurrent windings constituting theother side of the some, soicl windings being connected so that noalternating current will be generated in the direct current bus bar whenalternating current is supplied to said windings whereby a voltage willbe obtained in sold secondary circult proportional to the current in thebus bar, means for multiplying the output voltage of said soturoblereactor, means for rectifying said. multiplied voltage, means forobtaining a voltage in said secondary circuit proportional to thatrequired by the load and in opposition to said multiplied voltage, rindmeans responsive to the direction of current flow in said circuit forvarying the amount of direct current supplied to said bus bar.

3. A system for regulating the current output of a generator including,in combination, a. first circuit including a. bus bar connected to thegenorator for conveying the direct current generated thereby to theload, a second electric circuit including a saturable reactor with oneside thereof connected to the bus bar so that a direct currentproportional to that existing in the bus bar is provided therein withalternating current windings constituting the other side thereof, asource of alternatingcurrent supply for said windings, saicl windingsbeing connected so that no alternating current will be generated in thedirect current side of the suturable reactor when alternating current issupplied to said windings whereby a, voltage will be obtained in saidsecond circuit proportional to the current in said first circuit andsaid bus bar, a resistor connected in series with said windings, meansfor rectifying the voltage drop across said resistor, means forobtaining a. voltage in said second circuit proportional to thatrequired by the load and in opposition to said rectified voltage, andmeans responsive to the direction of current flow in said second circuitfor varying the output of said generator.

. ROBERT W. HOLMAN.

REFERENCES QL'TED The following, references are of record in the file ofthis potent:

UNITED STATES PATENTS Number Name Date 1,680,806 Schmidt Aug. 14, 19281,710,755 West Apr. 30, 1929 1,776,151 Hall Sept. 16, 1930 1,921,703Schmidt Aug. 8, 1933 1,994,324 Suits Mar. 12, 1935 2,137,043 Dawson Nov.15, 1938 2,325,401 Hurlston July 27, 1943 2,332,042 Shobert Oct. 26,1943 2,404,948 Croce July 31), 1946

